1. Field of the Invention
The present invention relates to a solar cell module and a method for manufacturing the same and more particularly to a wide variety of solar cell modules with high reliability in which a region including a photovoltaic element is processed, and a method for manufacturing the modules.
2. Related Background Art
The solar cells popularly used at present are those of the type using crystal-based silicon and of the type using amorphous silicon. Among others, the amorphous silicon solar cells, in which silicon is deposited on a conductive metal substrate and a transparent, conductive layer is formed thereon, are promising, because they are inexpensive and lighter than the solar cells of the crystal-based silicon, and they have good impact resistance and high flexibility. In recent years, the amorphous silicon solar cells have been mounted on roofs and walls of buildings, taking advantage of the lightweight property, the good impact resistance, and the flexibility, which are the characteristics of the amorphous silicon solar cells. In this case, a support member (reinforcing sheet) is stuck to a non-light-receiving surface of a solar cell with an adhesive, and the composite is used as a building material. This sticking with a support member increases the mechanical strength of a solar cell module, thus preventing warpage and distortion thereof due to change in temperature. Particularly, since they can capture more sunlight, installation thereof on a roof is desirably conducted. In applications to the roofs, the conventional methods involved procedures of mounting a frame on a solar cell, setting a stand on the roof, and installing the solar cells thereon; whereas the solar cell modules with the support member stuck can be installed as roof materials directly on the roof by bending the support member. This achieves great reductions in the cost for raw materials and in the number of working steps, whereby inexpensive solar cell modules can be provided. In addition, the solar cells become very lightweight, because neither the frame nor the stand is necessitated. Namely, the solar cells can be handled as metallic roof materials, which are drawing attention recently because of their excellent mountability, light weight, and excellent earthquake resistance.
For example, the roof material and solar cell combination module proposed in Japanese Patent Application Laid-open No. 7-302924 is excellent in mountability because it is used in the same manner as the ordinary roof materials; it is also easy to handle because conventional machines can be used. This solar cell module is, however, constructed in such a structure that the photovoltaic element is located in a flat portion of a laterally-roofed flat-seam roof material and is not deformed at all.
In recent years, however, the originality of individuals has become increasingly valued, and this tendency is also the case for the building materials and solar cells. In order to produce the solar cells or building materials that meet various needs and have a wide variety of shapes, it is necessary to ensure the workability of all the regions including the photovoltaic elements rather than to always keep the regions above the photovoltaic elements flat.
Japanese Patent Application Laid-open No. 8-222752 or No. 8-222753 or Japanese Patent Publication No. 6-5769 describes a corrugated solar cell module as an example responding to the need for variety. In either case, the photovoltaic element is arranged in a corrugated manner in order to increase utilization efficiency of light, and the manufacturing method thereof involves a procedure of sticking the photovoltaic elements to a steel sheet or the like worked in a corrugated sheet shape, with an adhesive.
On the other hand, there are reports on studies of the relation between a-Si:H (hydrogenated amorphous silicon) layer and strain thereof.
For example, Appl. Phys. Lett. 54 (17), 1989, pp. 1678-1680, "Electrical properties of hydrogenated amorphous silicon layers on polymer film substrate under tensile stress," reports a change of resistance in a dark state where a tensile force is applied to a single film of a-Si:H (0.5 .mu.m thick and mainly of i-type a-Si:H) deposited on a PET/substrate (100 .mu.m thick). The detailed contents of this report are as follows.
Under the tensile force, the a-Si:H layer gradually increases its resistance (reversible) because of the piezoresistance effect before 0.7% strain is reached; however, it experiences a quick increase (irreversible) of resistance after 0.7% strain has been exceeded, because weak Si-Si bonds are broken. However, the a-Si:H layer with increased resistance due to 0.7% or more strain can be restored by annealing at 150.degree. C. for one hour.
Further, J. Appl. Phys. 66 (1), 1989, pp. 308-311, "Effect of mechanical strain on electrical characteristics of hydrogenated amorphous silicon junctions," reports the piezojunction effect of a-Si:H having the pin junction. The detailed contents of this report are as follows.
When a-Si:H having the pin junction is distorted in parallel with the pin junction, 8% decrease of current takes place both in the forward direction and in the reverse direction under the tensile stress of 7500 .mu..epsilon. (in the dark state). Further, 8% increase of current occurs under the compressive stress of 7500 .mu..epsilon..
There is, however, nothing described as to specific stress on the photovoltaic element on the occasion of bending the photovoltaic element into the corrugated shape or the like in the above conventional techniques. Namely, they fail to describe either a displacement amount of substrate, a displacement amount of photovoltaic element, or a displacement amount of solar cell module. There is nothing described about the effect of the stress and deformation and about their reliability at all.
Under such circumstances, the production of solar cell modules in which the photovoltaic elements are shaped so as to be placed under stress or deformed has been avoided; if a module is shaped, the reliability in that shape must be always examined. Since many reliability tests must usually be conducted for one product (a worked shape), much time is necessary to make a commercially available product. This method is not suitable for bringing the product to the commercial stage at a speed that meets the need for present solar cells and building materials required to provide a wide variety of products.
As described above, the following points need to be met in order to produce a wide variety of solar cell modules with high reliability at higher speed.
(1) To define a specific, deformable region of the photovoltaic element on the occasion of work of the region including the photovoltaic element.
(2) To ensure long-term reliability where the photovoltaic element is deformed.